UC Santa Cruz strawberry research boosted by $2.5 million grant

SANTA CRUZ >> Until recently, organic strawberry growers had no choice but to move their crop from field to field to keep a step ahead of crippling soil diseases. But an increasing number of growers are turning to a new technique developed by UC Santa Cruz researchers — the first, and only, proven natural fumigation method to beat back the microbial maladies.

Aided by a new $2.5 million USDA grant, researchers hope to continue their work and create a toolkit for farmers to apply the natural fumigation method to the specific environment in which they grow their crop.

The technique developed by the team is called anaerobic soil disinfestation, or ASD. And with the most widely-used conventional fumigant, methyl bromide, recently banned, it may have potential well beyond organic strawberry fields.

HOW IT WORKS

Before a field is planted, a carbon-rich material such as mustard seed or rice bran is spread across the field and covered with plastic. As the carbon decomposes, it leeches oxygen out of the soil, creating a fermented environment rich with bacteria that are unfriendly to harmful pathogens, according to Carol Shennan, an environmental studies professor at UC Santa who leads the research team. Another benefit: The healthy bacteria stick around even after the plastic is removed.

“So it’s not just an immediate kill off of what’s there, but you actually have a very vibrant microbial community left that makes the soil more resistant to disease in the future,” Shennan said.

GAINING GROUND

Shennan and her team began research into the technique back in 2003 and immediately began seeing success.

“We got about 95 to 100 percent reduction in disease in the soil with that first experiment,” Shennan said. “That really surprised us.”

Once word of the promising results began to spread, farmers’ interest piqued.

“About five years ago we had one acre of strawberries being grown with the technique, and now it’s up to about 1,500 acres total,” Shennan said. “There was a lot of interest from growers.”

Strawberry growers are notoriously slow to adopt new methods because of the amount of up-front investment needed to produce a field of berries, according to Carolyn O’Donnell, who directs communications at the California Strawberry Commission.

“Strawberry farmers invest $20,000 per acre before they pick their first berry, so they don’t want to jump completely in on any system that they’re not convinced works,” O’Donnell said.

O’Donnell estimated up to 20 percent of organic strawberry farmers now fumigate their fields with the ASD method.

In Santa Cruz County, growers, including the world’s largest berry company, Driscoll’s, have already adopted ASD for at least some of their organic fields, according to Shennan.

BEYOND ORGANIC

The nation’s strawberry industry is valued upwards of $2.9 billion, and more than 80 percent of the berries are grown on California’s coast.

The industry grew to that size by fumigating its fields with methyl bromide, an odorless, colorless gas that was used to control a large number of pests.

Studies had found that exposure to the chemical caused damage to lungs, eyes, skin and the nervous system, but the end came for the chemical after it was linked to ozone depletion and it was banned by the EPA.

Two less-effective alternative fumigants are in use, according to O’Connell. But as the UC Santa Cruz team continues to perfect its new, natural technique, she said conventional farmers will soon come knocking.